The present invention relates generally to an optical element with variable optical properties and an optical device using the same, and more particularly to a variable hologram element and an optical device using the same.
Among optical elements so far known to have variable optical properties, there is such a liquid crystal lens arrangement 901 as shown in FIG. 23. A light beam incident from the left of the paper is merely converted through a polarizing plate 902 to polarized light, which is then incident on a liquid crystal lens 903. When the voltage applied on the liquid crystal 904 of the liquid crystal lens 903 is held off, liquid crystal molecules 905 are oriented as shown and the refractive index of the liquid crystal 904 is so increased that the liquid crystal lens can act as a convex lens. When the voltage is put on, the liquid crystal molecules 905 are oriented parallel to an optical axis 906, resulting in a decrease in the refractive index of the liquid crystal 904. This causes the convex lens action of the liquid crystal lens to become slender. However, a problem with this liquid crystal lens arrangement 901 is that the amount of light available is limited to about 40% due to the presence of the polarizing plate 902. In FIG. 23 reference numerals 907, 908 and 909 represent a transparent electrode, a switch and an AC source, respectively.